Conventionally, regarding ECU for an automotive vehicle, when a passenger or a driver operates a switch, electrostatic charge may penetrate into the ECU through a wiring harness, so that an IC in the ECU is damaged. Thus, to protect the ECU from the static charge, an electric part such as a resistor is formed on an input side of the ECU. The electric part for the protection of the ECU prevents not only the static charge but also external noise from penetrating into the ECU.
Further, recently, the number of electric parts in the ECU in the vehicle increases, and an accommodation space for the ECU becomes smaller. Thus, it is required to minimize the ECU and to increase the number of electric parts in the ECU.
Furthermore, to improve lifetime of a solder, an electrode is formed on a long side of the electric part in the ECU, instead of a short side of the part. In this case, a distance between electrodes becomes narrower, compared with a case where the electrode is formed on the short side of the part.
Thus, the electric part for the protection of static charge is minimized, and the distance between the electrodes of the parts becomes narrower so that a distance between lands on a circuit board becomes narrower, the lands corresponding to the electrodes. Therefore, conventionally, the electric part such as the resistor can prevent the static charge from penetrating into the IC of the ECU, i.e., the static charge penetrating into the IC is reduced. However, in the above device, since the distance between the lands is short, the static charge transmits between the lands through the protection part so that the static charge is not reduced in the protection part. Thus, the static charge directly penetrates into the IC so that the IC is damaged.
To protect the IC from the above direct transmission of the static charge, Japanese laid-Open Patent Publication No. S62-35480 discloses a circuit board. The circuit board includes the first wiring and the second wiring. The first wiring includes a resistor for limiting current, and formed on a signal input terminal side of a semiconductor circuit package. The second wiring works as a ground, and includes two parts, one of which protrudes and extends in parallel to the first wiring, the other one of which is connected to the semiconductor circuit package. The circuit board includes a protrusion facing the first and the second wirings so that a spark gap is provided. The spark gap is covered with a tape.
In general, a wiring is coated with an insulation film. Accordingly, in the device having the spark gap between the first and the second wirings, the static charge is not absorbed effectively, since the wiring is covered with the insulation film. Thus, the static charge may damage the IC.